Projected Sea Level Rise of Coastal Sunderbans

Indian part of the Sunder- bans, stands on the Hooghly-Matla estuarine complex, a type example of highly destructive tide-dominated delta, has faced wave vigour and tidal action twice daily in the semi-diurnal tidal situation. As a result, coastal dunes have gradually been eroded and the sediments are transported towards the sea side zone. The coastal Sunderbans is ornamented with the abundant linear sand bars formed due to accumulation of sands eroded away from the coastal dunes at present. But even in the eighties of the last century, coastal sand dunes stand in the supratidal zone protecting the inland area from the intrusion of saline water from the sea. Coastal dunes generally have not migrated and are formed with the association of a few halophytic herbs, creepers and grasses. These types of plants like Ipomoea pescaprae, Sesuvium portulacastrum etc assist the initiation and precise growth of the coastal dunes. The halophytic herbs and creepers arrest sands and help formation of mature dunes from an embryonic one. The roots and rootlets of these halophytic plants acting as sediment binders have manifold roles for the formation and stabilization of dunes.

Of late waves of greater heights on the coastal Sunderbans thrash the coastline dashing those sand dunes. Coastal Sunderbans once studded with lines of sand dunes in the Henry Island, Fedrick Island, Bakkhali, Fraserganj, Baliara of Mousuni Island, Gangasagar of Sagar Island faces destruction for wave action as a result of sea level rise due to climatic change increasing water height due to sea level rise makes the differences as the vigour of wave remain almost the same as the Geological Survey of India reported on the wave parameters of the coastal stretch of Digha—Sankarpur, adjacent to the coastal Sunderbans.

Huge water mass thrash the coastal dunes and even the vigour of wave have gradually been increasing due to sea level rise as a result of climate change. Sea level rise gradually been rising as Till J J Hanebuth reported that the global sea level is considered to have been stable during the 18th century, while it is assumed an overall eustatic rise of 60 mm in the 19th century and 190 mm in the 20th century

The projected global sea level rise including the areas of the coastal Sunderbans at the end of the 21st century varies from 1 ft to 4.3 ft, which would inundate the entire coastal Sunderbans areas. Remedial measures should be taken much well before facing such panic incidents as a result of sea level rise, particularly for the denizen of the people living in the coastal areas of the Sunderbans.

Wave Parameters                             Data Collected
Average Wave Height (H)                49 cm
Average Wave Period (T)                 17 cm
Average Wave Length (L)               
at a water depth of 1.5 m               65.21 m
Wave Steepness (H/L)                     0.065
Surf Scaling Factor (?)                      4.60
Wave Energy (E)                               282.5
Average Beach Slope                      0.450 to 1.430 (<50)
Average Beach Width                     80 m to 290 m
Grain Size                                        Fine grained sand admixed with clay silt

Global Sea Level Rise
Time Period                                    Sea Level Rise
18th Century                                    Stable
19th Century                                    60 mm
20th Century                                   190 mm
21st Century            31 to 1311 mm (Projected)

 [contributed]

Frontier
Vol. 51, No. 49, Jun 9 - 15, 2019